Plastic container having a high resistance to chemical attack and method of making same

ABSTRACT

A plastic container has a high resistance to chemical attack and is made by a method including extruding and inflating a tube in a single operation by a coextrusion blow molding process to form a hollow plastic body. The tube consists of an outer layer made of glycol-modified polyethylene terephthalate (PETG) and an inner layer made of polyethylene terephthalate (PET), polyethylene naphthalate (PEN) or a mixture thereof. Selection of the foregoing materials and layers allows the plastic body for the container to be made in a single operation by coextrusion blow molding.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a plastic container of a high resistance tochemical attack and to a method for producing a the plastic container.

2. Prior Art

The fundamental problem exists of furnishing an inexpensive, easy-to-useplastic container with high chemical resistance and a highly protectiveeffect against oxygen for oxygen-vulnerable products to be contained,such as permanent-waving preparations based on ammonium thioglycolate,hair dyes with ammonia or monoethanolamine, temporary hair coloringswith direct-drawing pigments based on emulsions, cosmetic hair productswith alcohol in a proportion of greater than 30%, and cosmetic hairproducts with a low pH of less than 4.

It is true that (extrusion blow molded) hollow bodies of PVC with highchemical resistance are known, but they are deficient in theirecological properties and limitations in certain recyling processes. Inaddition, (extrusion blow molded) hollow bodies of modified polyethyleneterephthalate (PET) are known. From glycol modification, for instance,these modified polyesters have a higher melt viscosity, to lend themadequate tube stability for the extrusion blow molding process. Whenthis material is used for the above products to be contained, however, achemical attack takes place, which can lead to embrittlement, clouding,softening, and stress cracks.

Using pure polyethylene terephthalate (PET) is possible only in thoseblow molding processes in which the preform can be made by injectionmolding, since the melt viscosity is too low for processing by extrusionblow molding. Although there is indeed chemical resistance, neverthelessbecause of the injection blow molding process, developing and realizinga hollow body of this kind entails major investment for tools, longdevelopment lead times, major effort if the shape of weight of thehollow bodies is to be changed, and high production runs of at least 1million pieces per year, because of the commercial requirements of theprocess.

In contrast to PET, using polyethylene naphthalate (PEN) also provideshigh chemical resistance against hair dyes, but even PEN has to beprocessed by injection blow molding, and thus has all the disadvantagesnamed above for PET.

The use of multilayer hollow bodies based on polyolefins, such as PE/PA,is also possible, but with the following disadvantages: swelling of thePE, pigment creepage into the PE, problems with the welding seams in thehollow body, and the fact that adequate transparency if needed cannot beattained. The process is also expensive, because of the three layers andthe adhesion promoter that has to be used.

From German Patent Disclosure DE 44 15 549 A1, an extrusion blow moldedthree-layer hollow body is known whose layers (from the inside out)comprise PETG, adhesion promoter and polyolefin. Only a water vaporbarrier and a creepage barrier are achieved here. The disadvantages ofthe three-layer process, as described above, still pertain. Transparentcontainers cannot be produced. Nor is adequate chemical resistanceachieved.

In addition, extrusion blow molded two-layer hollow bodies are known,which comprise two materials with affinity for one another, selectedfrom the same group of materials, and which therefore require noadhesion promoter. These hollow bodies are used for instance when makinga glossy layer on polyolefin bodies. In that case the main wall is blownfrom a nonglossy polyolefin with high melt viscosity, and a glossy layerof the same or similar material with low melt viscosity is then appliedby the coextrusion blow molding process.

SUMMARY OF THE INVENTION

The object of the invention is to provide an improved plastic containerhaving a high resistance to chemical attack, which has a highlyprotective effect against oxygen for oxygen-vulnerable products to becontained, and which is ecologically unproblematic and can be producedeconomically.

It is also an object of the prevent invention to provide an improvedmethod of making a plastic container having a high resistance tochemical attack, which is more economical than prior art methods and inwhich dimensional changes are easier to make.

According the invention the economical method of making a plasticcontainer includes extruding and inflating a tube in a single operationby a coextrusion blow molding process to form a hollow plastic body,wherein the tube consists of an outer layer and an inner layer. Theouter layer consists of glycol-modified polyethylene terephthalate(PETG) and the inner layer consists of polyethylene terephthalate (PET),polyethylene naphthalate (PEN) or a mixture thereof.

The plastic container of the invention comprises a hollow plastic bodyconsisting of an inner layer and an outer layer. The outer layer isglycol-modified polyethylene terephthalate (PETG) and the inner layerconsists of polyethylene terephthalate (PET), polyethylene naphthalate(PEN) or a mixture thereof.

In other words, this involves a two-layer hollow body with a base layerof extrusion blow moldable modified PET, preferably glycol-modified PETGwith high melt viscosity, with sufficient melt strength to allow theextrusion of a hanging tube, and with an inner protective layer of amaterial of higher chemical resistance that adheres well to the tube andis selected from the group of polyester materials of the same affinitycomprising unmodified PET, a mixture of PET and PEN, or PEN of low meltviscosity.

As a result of this embodiment, the advantages of PVC without itsdisadvantages are attained; specifically, a chemically resistant,oxygen-impermeable hollow body is available that is ecologicallyunproblematic, easily recycled, and optionally transparent and glossy,and that at the same time makes economical production possible even forlower production runs, at low tool cost, with short production times andeasy variability of the dimensions of the hollow body (shaping) andadjustment of the weight (wall thickness).

BRIEF DESCRIPTION OF THE DRAWING

The objects, features and advantages of the invention will now beillustrated in more detail with the aid of the following description ofthe preferred embodiments, with reference to the accompanying figures inwhich:

FIG. 1 is a side view of an exemplary embodiment with a releasableclosure;

FIG. 2 is a refinement of the function of the closure; and

FIG. 3 is an extruded, hanging tube as a preform.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1, a hollow plastic body 1 which has an inner layer 2 and anouter layer 3 is shown. The outer layer 3 comprises modifiedpolyethylene terephthalate (PET), preferably glycol-modifiedpolyethylene terephthalate (PETG), and the inner layer 2 comprisespolyethylene terephthalate (PET) or polyethylene naphthalate (PEN) or amixture of polyethylene terephthalate and polyethylene naphthalate.Preferably, the outer layer 3 makes up a proportion of more than 50% ofthe total layer thickness 4, and the inner layer 2 makes up a proportionof less than 50%. In this exemplary embodiment, the hollow body 1 isembodied as a bottle 5, which is provided with a closure 6. As theclosure 6, a twist-off cap, not shown, or a re-releasable closure 7(screw top, snap-type or hinged closure) may be provided. A good sealingproperty of the releasable closure 7 is obtained by providing theclosure with a sealing layer 8, which comprises an identical or similarinner layer 2 and outer layer 3 and is optionally elastic in shape (forinstance by means of a suitable additional coating or a disk), for thesake of better form-locking pressing against a rim 9 of the bottleneck.The result is very good sealing properties, because the inner layer 2 ofthe bottle 5 is in force-locking engagement with the inner layer 2.1 ofthe sealing layer 8 of the releasable closure 7.

An advantageous refinement of the closure function is shown in FIG. 2,in which the rim 9 of the bottleneck is embodied as flangelike ortrumpet-like, in such a way that the inner layer 2 of the bottle is inforce-locking engagement with the inner layer 2.1 of the sealing layer 8of the releasable closure 7 over a relatively large surface area, theresult of which is even an better sealing property.

FIG. 3, in a sectional view, shows a hanging tube 10 extruded from anextruder 11. It is clear from this illustration that despite the lowmelt viscosity of PET, the inner layer 2 is joined in laminar fashion tothe inner surface of the outer layer 3, or as if glued to it, and thusthe outer layer 3 functions as a supporting layer for the inner layer 2,since the outer layer 3, for instance because of PETG, has a higherviscosity and thus increased melt strength. For the first time, thismakes it possible to employ a conventional economical extrusion blowmolding process, since the time elapsed between the extrusion and theblow molding is so short that the inner layer 2 is essentially incapableof spreading (downward) along the inside of the outer layer 3.

The method for producing hollow plastic bodies 1 with an inner layer 2and an outer layer 3 by an extrusion blow molding process isdistinguished in that the outer layer 3, comprising modifiedpolyethylene terephthalate (PET), and the inner layer 2, comprisingpolyethylene terephthalate (PET) or polyethylene naphthalate (PEN) or amixture of polyethylene terephthalate and polyethylene naphthalate, areput together in a single operation in the production process by acoextrusion blow molding process and are extruded and inflated in theform of a tube 10; preferably a glycol-modified polyethyleneterephthalate (PETG) is provided. Until the blow molding process begins,the tube 10 hangs essentially freely.

List of Reference Numerals

1 Hollow plastic body

3, 2.1 inner layer

3, 3.1 Outer layer

4 Total layer thickness

5 Bottle

6 Closure

7 Releasable closure

8 Sealing layer

9 Rim of the bottleneck

10 Tube

11 Extruder

We claim:
 1. A plastic container that is resistant to chemical attack,said plastic container being made by a method comprising coextrusionblow molding of a hollow plastic body (1) in a single operation and saidplastic container comprising said hollow plastic body (1), wherein saidhollow plastic body consists of an inner layer (2) and an outer layer(3), the outer layer (3) consists of glycol-modified polyethyleneterephthalate (PETG) and the inner layer (2) consists of polyethyleneterephthalate (PET), polyethylene naphthalate (PEN) or a mixturethereof.
 2. The plastic container as defined in claim 1, wherein saidhollow plastic body has a total layer thickness, said outer layer (3)has an outer layer thickness, said inner layer (2) has an inner layerthickness and said outer layer thickness is more than 50% of said totallayer thickness while said inner layer thickness is less than 50% ofsaid total layer thickness.
 3. The plastic container as defined in claim1, further comprising a closure (6,7) for said hollow plastic body, andwherein said hollow plastic body is embodied as a bottle (5).
 4. Theplastic container as defined in claim 3, wherein said closure (6,7) isreleasable and includes a sealing layer (8), said sealing layer (8)comprising an inner closure layer (2.1) and an outer closure layer(3.1).
 5. A method of making a plastic container, said method comprisingextruding and inflating a tube in a single operation by a coextrusionblow molding process to form a hollow plastic body, said tube consistingof an outer layer and an inner layer, and wherein said outer layerconsists of glycol-modified polyethylene terephthalate (PETG) andwherein said inner layer consists of polyethylene terephthalate (PET),polyethylene naphthalate (PEN) or a mixture thereof.
 6. The method asdefined in claim 5, wherein said tube is freely hanging during saidcoextrusion blow molding process.